Unsharp mask in electronic color correction



Aug. v. c. Q UNSHARP MASK IN ELECTRON 1 C COLOR 'CORRECTiON Filed March10, 1948 2 Sl-IEETS-Sl-IEET 1 28 BLQE W 34 5 I 3 PRE- LINEAR VAR/ABLEMASK F AMPLlF/ER AMPLIFII2 coMPI2ss4 MODULATOR J 4 i E I F/XED MAI6 l I58! COMP/25550? :i 29 1/32 35 40, l I n PRE- LINEAR VARIABLE MASKAMPLIFIER *AMPL/FIR' c0MP/ass1l MODULATOR i i I I I ED II n I, E 30 R 5355 3 7 5, 8 3: 9 i u PRE- LINEAR VARIABLE M4sK I AMPLIFIER AMPLIFIERcompass MODULATOR l I I l 1 l l 4 1/ i i jg 7 W i ll I 59 $60 6/ mmmm, ll V I w M I41? "2'"? I Z6 I -I- /2 II 27. I I.

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VINCENT c. HALL HIS ATTORNEYS.

Aug. 5, 1952 v. c. HALL 'UNSHARP MASK IN ELECTRONIC COLOR CORRECTIONFiled March 10,. 1948 2 SHEETS-SEE! 2 TO MASK/NC AMPLIFIERS AND WIRERECORDERS TO S-IGNAL AMPLIFIERS INVENTOR- VINCENT C. HALL HIS ATTORNEYS.

Patented Aug. 5, 1952 UNSHARP MASK IN ELECTRGNIC COLOR CORRECTIONVincent C. Hall, Stamford, Conn assignor to E'ime, Incorporated, NewYork, N. Y a corporation of New York Application March 10, 1948, SerialNo. 14,007

The present invention relates to electronic color correstion systems andmore particularly to new and improved systems of this character in whicha technique known as unsharp masking is employed to effect colorcorrection.

Color correction by masking is a well known procedure in colorphotography. It comprises essentially superimposing, in register, a highor normal contrast separation negative and a low contrast positive.Electra-optical systems embodying means for incorporating the maskingprocedure in making color separation negatives are also well known inthe art.

It has been discovered that by using an unsharp mask, 1. e., one lackingin fine detail to some extent, a marked improvement in the degree ofcolor correction achieved results. In particular, the degree of registerrequired is not so close as where extremely sharp masks are used. Thisis of no importance where the masking is accomplished electronically.However, in both mechanical and electronic masking systems, the use ofunsharp masking results in considerable improvement in contrast in areasof fine detail. The advantages of using an unsharp mask to provide colorcorrection are discussed in an article by J. A. C. Yule (Phot. Soc. ofAm. Journal, March 1945) and references to previous work in this fieldare given.

The object of the present invention is to provide new and improvedelectro-optical color correction systems in which the advantages ofunsharp masking are obtained.

Another object of the invention is to provide new and improvedelectronic color correction systems of the above character in whichelectric signals are produced which represent variations in one color ofa subject being scanned and are modified by other electric signalsrepresenting an unsharp mask of another color in the subject.

According to the invention, a subject in color is scanne by two diiiernt scanning apertures,

one of which is larger than the other so as to lose fine detail to theextent required to give the desired degree of unsharpness. Where theterm scanning aperture is used herein, it is intended to mean the areaof the colored original that is actually viewed by the'scanningmechanism at any instant. Both of thebeams corresponding to the twoscanning apertures are split into a number of color components asdesired and electric signals corresponding thereto are produced, anysuitableapparatus being used for this purpose. The electric signalscorresponding to the smaller scanning area are then" modified 12 Claims.(oi. 178-52) by the signals from the larger scanning area, according toknown laws, to produce separation negatives embodying masking colorcorrections.

According to the invention two scanning apertures of relatively smalland relatively large area, respectively, are provided. The two scanningapertures are spaced apart any suitable distance along the scanning lineand each aperture has a separate .beam splitting and electric signalproducing system. Signal delaying means are provided in this embodimentfor eliminating phase differences between the two sets of signalsproduced by the two systems, resulting from the spacing between the twoscanning apertures. Scanning at two difierent positions spaced apartalong the scanning line may also beaccomplished by using a singlescanning aperture of relatively large area in conjunction with maskingmeans for obtaining from the single scanning aperture two beamsrepresenting, efiectively, two scanning apertures of different sizes.

Additional objects and advantages of the invention will be apparent fromthe following detailed description of several typical embodiments, takenin conjunction with the accompanying drawings, in which:

Figure 1 is a schematic diagram or" a portion of an electronic colorcontrol system constructe according to the present invention;

Figure 2 illustrates schematically a form of signal delaying device foruse with the system shown in Figure 1; and

Figure 3 is a schematic diagram of a modified form of scannerconstructed according tog'the invention.

In the system illustrated in Figure ,1, the subject It! to be scanned (aKodachrome transparency, for example) is shown mounted on a transparentscanning drum II which is adapted to be advanced both longitudinally andin rotation by any suitable means such as a conventional lead screwlZdriven by a motor-l3. The scanning drum ii may be made. of-sufiicientlength to accommodate four separation negatives I4; l5,

l6 and IT to be made by'means of the electronic color correctionsystemshown, orxthe negatives -may be mounted on separate scanning drums tionsalong the 'scanning lineby 'two scanning apertures, one of which i-larger than the other.

Thus, light interrupted periodically byasuitable light chopper 12 isdirected froma'suitable source i 8 through a lens system 9 thetransparency l0. Associated with the lens system 19 is an opaquediaphragm 20 having a relatively small aperture 2| therein through whichlight can pass. In a representative scanning system, the aperture 2|might be made square in shape and its dimensions might be selected tocorrespond to a scanning aperture approximately .004 inch on a side fora system scanning 250 lines per inch. As stated, the scanning apertureis the actual area of the original ID that is viewed by the scanningsystem at any instant- Spaced apart from the light source 18 along thescanning line is a second light source 22 which directs lightinterrupted periodically by a second light chopper 13 through a lenssystem 23 to another point on the transparency Ill located a givendistance away along the scanning line from the light focused on thetransparency in by the source I 8. Although the two scanning points onthe transparency 10 are shown 180 apart in Figure 1 by way ofillustration, obviousl'y they may be located any suitable distanceapart.

Associated with the lens system 23 is an opaque diaphragm 24 having anaperture 25 formed therein. The aperture 25 may be either square orcircular in cross-section and its size may be selected to correspond toa scanning aperture approximately .008" by .008" if square, or .008" indiameter, if circular, for example. The aperture 25 provides a beam forproducing an unsharp masking signal to be employed in an electroniccolor correction system, as described in greater detail below.

The beam of light transmitted through the transparency l0 fl'om the lenssystem I9 may be directed by a reflector 26 to another reflector 21providing'a beam which is split up into a plurality of com onents in anysuitable manner as by the prisms 28, 29 and 30, for example. The threeb'eam's to'rmea by the prisms 28, 29 and so are transmitted throughblue, green and red filters 3h, 32 and 33, respectively, and thefiltered light ic dire'cte'd to suitable photosensitive devices 34, '85and 36, respectively.

The output of the photosensitive device 34 is 'fedto one channel of aconventional electronic c'olor correction system which may include apreamplifier 31, a linear amplifier 38, a variable compressor 39 and amask modulator '40. The I eutputs of the photosensitive devices 35 and36 are fed to similar channels, and corresponding elements thereof aredesignated by primed and double-primed reference characters,respectively.

In similar fashion, the beam of light transmitted through thetransparency In from the lens system 23 may be directed by thereflectors 4| and 42 to any suitable beam splitter such as the prisms 43and 44, for -example. The two beams formed by the prisms 43 and 44 aretransmitted through red and :green filters 45 and 46, respectively, and,impinge upon photoelectric cells 41 and 48 i'" e'spectively.

- Since the two scanning beams from the light sources 18 and 22,respectively, are spaced apart along the scanning line, the electricsignals corresponding thereto must be adjusted to bring -them in phasebefore they are combined in the ure 1).

The delay device shown in Figure 2 may comprise a wire or tape 49 madeof magnetic material mounted on a drum 50 driven either by the sameshaft which drives the scanning drum II, or driven in synchronismtherewith. The wire 49 is adapted to be magnetized by a coil 5|connected to the output of the preamplifier 52 (Fig- Spaced apart fromthe energizing coil 51 an angular distance equivalent to the angularspacing between the two beams impinging upon the scanning cylinder II isa pick-up coil 53. The pick-up coil 53 is preferably made adjustable inposition with respect to the energizing coil 5| so that a range ofdifferent delay times can be accommodated. A suitable erasing coil 58may be mounted adjacent the wire 49 for the purpose of erasing thesignal thereon after it ha passed the pick-up coil 53. V

The output of the pick-up coil 53 may be supplied to a linear amplifier54, compressed in a variable compressor 55 and fed by means of asuitable coupling tube 56 to a fixed mask compressor 51. The maskcompressor 51 supplies an output to the green mask modulator 40, in suchfashion as to produce an electrical output there from corresponding tothe modification of the green signal by an unsharp mask of the red.

In similar fashion, the output of the photosensitive device 48(Figure 1) may be fed to a preamplifier 52, the output of which may bedelayed by a wire drum mechanism 50 like the wire drum 50, and amplifiedin a linear amplifier 54. The output of the amplifier 54 may becompressedin a suitable variable compressor 55 and fed through acoupling tube 56' to a fixed mask compressor 51' which supplies anoutput to the mask modulator 40 in the blue channel. It will beunderstood, therefore, that the output of the modulator 40 will be ablue signal modified by the equivalent of an unsharp mask of the greensignal.

The outputs of the mask modulators in the three color channels may befed through conventional color correction circuits (not shown) toprovide signals for actuatin the glow lamps 58,

manner.

In the modification shown in Figure 3 of the drawings, a somewhatsimpler optical system is employed. In this modification, a light source62 is placed within the scanning drum H and directs light through anaperture 63 in an opaque diaphragm 64 to a relatively wide apertureoptical system 65, which focuses a relatively wide beam on the film III.For example, the aperture 63 may be square and its dimensions may beselected to correspond to a scanning aperture .01 by .02 inch.

The beam of light falling upon the transparency In may be subsequentlyenlarged by an appropriate optical system 66 and separated into largerand smaller scanning areas aligned along the scanning direction by theapertures 61 and 6-! formed in a diaphragm 69. The two beams may bedirected in any suitable manner, as by the prisms 10 and II, forexample, to conventional beam splitter systems as described above inconnection with Figure 1.

It will be understood from the foregoing description that the inventionprovides novel electronic color correction systems for providing aneffect equivalent to unsharp masking. By scanning a transparency withscanning apertures of different area, a picture signal and a maskingsignal can be obtained, which can be combined electronically to producea signal corresponding to a signal of given color modified by theequivalent of an unsharp mask of another color.

Further, by utilizing a conventional wire or tape recorder with thesespaced apart scanning apertures to bring the two scanning signals intophase, any amount of unsharpness found desirable can be used. Since theamount of phase delay is adjustable, it is possible in setting up theapparatus to allow for construction errors. Once the apparatus has beenset, however, the proper phase adjustment is always made. Also, theunsharp masking signal is obtained without producing any loss in lightintensity in the main signal channel.

It will be further understoodthat since a relatively larger aperture isemployed in the masking channel the band of frequencies which it isrequired to amplify is much narrower so that the optical requirementsfor the masking channel are much less severe than those imposed upon themain signal channel.

The several embodiments described in detail above are intended to bemerely illustrative of the invention. Numerous changes within the spiritof the invention will become readily apparent to those skilled in theart. For example, although a cylindrical scanning drum has been shown,obviously the invention can be applied to a system employing a flatplate which carries the colored original. The several embodiments shownare susceptible of other modifications in form and detail within thescope of the appended claims.

I claim:

1. In a scanning system, the combination of a subject embodying visualintelligence to be scanned, first means having a scanning aperture offixed size for scanning elemental areas of said subject to provide firstelectric signals rcpresentative of variations in said intelligence,second means having a scanning aperture of fixed size for scanning saidelemental areas of the subject at a position spaced apart along thescanning line from the scanning position of said first scanning means toprovide second electric signals representative of variations in saidintelligence, and means for modifying values of one of said first andsecond electric signals as a function of values of the other of saidsignals derived from scanning essentially the same areas of saidsubject.

Z. In a scanning system, the combination of a subject embodying visualintelligence to be scanned, first means having a scanning aperture offixed size for scanning said subject to provide first electric signalsrepresentative of variations in said intelligence, second means having ascanning aperture of fixed size for scanning said subject at a positionspaced apart along the scanning line from the scanning position of saidfirst scanning means to provide second electric signals representativeof variations in said intelligence, means for delaying said firstelectric signals for a sufiicient time to bring first and secondelectric signals corresponding to a predetermined point of said subiectsubstantially in phase, and means for modifying said second electricsignals by said delayed first electric signals.

3. In a scanning system, the combination of a subject embodying visualintelligence to be scanned, first means for scanning said subject withan aperture of given size to provide first electric signalsrepresentative of variations in said intelligence, second means forscanning'said subject with an aperture of different fixed size at aposition spaced apart along the scanning line from the scanning positionof said first scanning means to provide second electric signalsrepresentative of variations in said intelligence, means for delayingsaid first electric signals for a sulficient time to bring first andsecond electric signals corresponding to a predetermined point of saidsubject substantially in phase, and means for modifying said secondelectric signals by said delayed first signals.

l.- In an electronic color correction system, the combination of asubject in color to be scanned, first means for scanning said subject toprovide first electric signals representative of variations in acolor'of said subject, second means for scanning said subject at aposition spaced apart along the scanning line from the scanning positionof said first scanning means to provide second elec tric signalsrepresentative of variations in a color of said subject, means fordelaying said first electric signals, and means for modifying saidsecond electric signals by said delayed first electric signals.

5. In an electronic color correction system, the combination of asubject in color to be scanned, first means for successively scanningareas of given size of said subject along a scanning line to providefirst electric signals representative of variations in a color of saidsubject, second means spaced apart from said first scanning means alongsaid scanning line for successively scanning areas of greater size ofsaid subject to provide second electric signals representative ofvariations in a color of said subject, means for delaying electricsignals produced by the leading scanning means, and means for combiningsaid delayed electric signals and the electric signals produced by thelagging scanning means.

6. In an electronic color correction system, the combination of asubject in color to be scanned, first means for successively scanningareas of given size of said subject along a scanning line to providefirst electric signals representative of variations in a color of saidsubject, second means spaced apart from said first scanning means alongsaid scanning line for successively scanning areas of greater size. ofsaid subject to provide second electric signals representative ofvariations in another color of said subject, means for delaying electricsignals produced by the leading scanning means for a sufficient time tobring first and second electric signals corresponding to a predeterminedpoint of said subject substantially in phase, and means for combiningsaid delayed electric signals and the electric signals produced by thelagging scanning means.

7. In an electronic color correction system, the combination of asubject in color to be scanned, first means for scanning said subjectwith an aperture of relatively small size to provide first electricsignals representative of relatively finely detailed variations in acolor of said sub ect, second means for scanning said subject with anaperture of relatively greater size at a position spaced apart along thescanning line from the scanning position of said first scanning means,to provide second electric signals rep-' resentative of less finelydetailed variations in another color of said subject, means for delayingone of said first and second signals for a sufficient time to bring saidfirst and second signals substantially into phase, and means formodifying theumlelayed oneof said first and second. signals bythedelayed other of said signals, whereby an. output representative ofvariations in one color of said subject, masked by an unsharp mask ofanother color is produced.

8. In a-method of scanning asubject embodying visual intelligence .to bescanned, the steps of scanning areas of said subject with scanning areasof fixed sizes that are spaced. apart along the scanning line to providefirst electric signals representative of. variations in saidintelligence and second electric signals representative of variations insaid intelligence, respectively, delaying. oneof said first and second.signals to bring. said. signals in phase, and modifying said. firstelectric signals.- inaccordancewith said sec.- ondelectric signals.

9. Infiamethodofscanning a subjectembodying visual. intelligence to. bescanned, the steps of. scanningareas of said subject with scanning.areas of different fixed sizes that are spaced apart along the scanningline to provide first electric signals representative of relativelyfinely detailed variations insaid intelligence and second electricsignals representative of. relatively less finely detailed variations insaid intelligence, respectively, delaying one of said first and secondsignals to bring said signals substantially in phase and modifying theundelayed one of said signals in accordance with the other delayedsignal.

10. In a method of reproducing a subject in color, the steps of scanningareas of said subject with scanning areas of different sizes thatarespaced apart along a scanning line to provide first electric signalsrepresentative of relatively finely detailed variations in one color ofsaid subject and second electric signals representative of less finelydetailed variations in another color of said subject, delaying one ofsaid first and second electric signals to bring said signalssubstantially in phase, and modifying the undelayed one of said signalsin accordance with the delayed one of said signals to produce an outputrepresentative of variations in said one color of the subject masked byan unsharp mask of said another color.

11. In a scanning system, the combination of a subject to be scanned, asource of light, an optical system directing a beam of light ofrelatively large area from said source to said subject, diaphragm meansin the-path of light from said beam that has been modified by saidsubject and having apertures of fixed sizes therein providing aplurality of scanning beams of different sizes spaced apart in thescanning direction, a plurality of photosensitive means disposed toreceive said scanning beams and to provide first electric signalscorresponding to variations in one of said scanning beams and secondelectric signals corresponding to variations in another of said scanningbeams, and means for modifying one of said first and second electricsignals as a function of the other.

12. In an electric color correction system, the combination or a subjectin color to be scanned. a source of light, an optical system directing abeam of. light of relatively large area from said source to saidsubject, diaphragm means in the path of light from said subject andhaving apertures therein providing a plurality of scanning beams ofdifferent sizes spaced apart in the scanning direction, a plurality ofphotosensitive means disposed to receive said scanning beams and toprovide first electric signals representative of variations in a colorpresent in one of said scanning beams of given size and second electricsignals representative of variations in a color present in another ofsaid scanning beams of larger size, and means for modifying one of saidfirst and second electric signals as a function of the other.

VINCENT C. HALL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,877,844 Gerlach Sept. 20, 19321,901,034 Karolus Mar. 14, 1933 2,165,168 Hardy July 4, 1939 2,185,139Wurzhrirg Dec. 26, 1939 2,231,669 Hall Feb. 11, 1941 2,253,086 MurrayAug. 19, 1941 2,286,730 Hall June 16, 1942 2,313,542 Hall Mar. 9, 19432,313,543 Hall Mar. 9, 1943 2,413,706 Gunderson Jan. 7, 1947 2,415,051Thompson Jan. 28, 1947 2,423,769 Goldsmith July 8, 1947

